Effector stowage or parking idea for Delta

One of the downsides of 0.9° steppers is that they don't seem to have the holding torque when unpowered - as they are after a print is finished. As a result of upgrading to 0.9° steppers on my delta printer the effector, along with its still hot hotend, will descend and rest on a newly finished print, occasionally sticking to it.
There are obviously a lot of ways around this. The end of print code could be set to give a long enough pause after print completion to allow the hotend to cool before disabling the steppers; some friction could be introduced to help the un-powered stepper holding torque to keep the effector up; a magnetic catch could give some extra upward force right at Z max etc..
Having seen this as a problem however, it did occur to me that having some form of parking/stowage for the effector would also be good for transport as the effector would not be free to collide with other bits of the printer as it is being bumped about
In the drawing below the effector is held up by a latch made of springy wire. At the beginning of a print job and just befor the call for the effector to move down the un-latch solenoid would be briefly powered and the latch solenoid would be powered at the end of the print job.

This could obviously be simplified by having only one solenoid. This would however need some stomping about in firmware to ensure that the first down movement after any Z-Home command would also cause the un-latch solenoid to be operated.

Here is my suggestion. At the end of printing, move the effector to a position a little outside the normal print radius (use M564 S1 to allow this if using RepRapFirmware), to the side of one of the towers and at the maximum height possible for that position. Then drop it a few mm so that a hole in the effector mates with a bracket or piece of piano wire attached to the tower, to prevent the effector from falling.

The standard homing sequence will lift the effector clear of the bracket or wire again.

My very first thought was the same as dc42, a simple bracket to simply park the effector on. Anything motorised is just overly complicated.

However, what would be wrong with magnets? 3 magnets on the upper brackets of the towers and 1 in each carriage means that when you are at the upper limits of Z, they simply attach to the magnets. The motors should be strong enough to detach themselves. Use magnetic arms for transport so they can be detached from the machine quickly, or have a latch at the top of the towers as well so that each carriage can be securely latched in place.

Thanks dc42 and Origamib. I originally though of something like that but did not think it through as I started thinking about transport stowage.

So if the effector is lifted to Z max and down maybe 5mm (to avoid triggering the upper limit switches), then moved to something like G0 X10 Y0 (where X and Y are the middle of their ranges) then down another maybe 3mm to park on a pin with a magnet to hold it down. On first homing the effector will always go straight up so will not bind on the pin.

My concern with using magnets to simply hold the effector up was that they may hold it just sufficient in its downward journey to give lost Z steps. Holding the effector down against a magnet would not give rise to lost steps.

That sound simple and needs little more than a few sequences at the end of the print G code.

If using RRF I'd set hotend to cool but wait for cooling, then descend and gently park somewhere nozzle to bed near the edge, in case it leaves a blemish over time.

What motors are you using Mike? My kossel XL uses 0.9 degree steppers and it does not descend after powering off, but I do use a sturdy keychain retractor to keep my umbilical, nimble, drive cable and water cooling tubing in a nice arc so its not resting on the effector.

The motors that I used were JK42HM 0.9° 42x42mm from Etang. Although I think that 0.9° steppers probably do have lower unpowered holding torque, I think my main problem is that the linear bearings got dirty when I had the printer stripped. I washed them in alcohol in an ultrasonic bath and lubricated them with sewing machine oil as the only grease I had was very viscous. I also tweaked the rails into the very best alignment I could get.

I think the answer to the droop is to re-grease the bearings with my thick grease but I may pursue the effector stowing on my long delayed hot delta.

I use 0.9deg motors too. They are 48mm long and their detent torque is sufficient to support the weight of the smart effector including one 40mm x 10m print cooling fan. However, if the effector is a long way off centre when I power down, then the highest carriage sometimes drops a bit. I guess if I added more weight such as a RDD extruder then I might have the same problem.

Your magnets only need to be strong enough to keep the arms up when in close proximity to them and this will stop the magnets causing pull on the carriages as they get close during printing.

If the difference between rising and falling is the friction caused by thick or thin grease, you'll only need some weak magnets. You could experiment with magnet strength by placing more or less material between the magnets. These magnets could easily be embedded in the prints as well.

Overall the effector is respectably light although the effector plate itself could be lightened, all other bits are as light or lighter than any I have come across. The problem seems to be as I stated though, the motors don't have much unpowered holding torque and I have got the bearings running so freely that power off means effector comes down.

I have something working now and so far it looks good. This is a slight modification of the method suggested by dc42 but just made with a length of 1.2mm piano wire and some end of print instructions. I would have done a photo or video but the workshop is too damn cold so I have stayed in the warm and done a diagram.

The effector is homed then moved down just a couple of millimeters and toward the front of the printer by a short distance so that the hook rests above the bar of the trapeezy thing. the motors can either be disables or the effector can be moved down a few more mm to ensure engagement first.

There doesn't seem to be any problems with the bits interfering with rods, Bowden tube or wires, nor is the print volume effected as everything happens in the non-printable part of the swept volume. End of print instructions should be relative to the Z home position if you setup alters the Z max value - such as auto leveling and different build stage thicknesses.

Please guys it may not be the (over)engineered solution you seek, but a keychain retractor is the answer. Very simple costs £2, works.

The way I use it is secured to the wiring loom, water cooling tubing, so it holds the effector up indirectly and keep my cable in a nice loop above the effector but you could attach it directly to the effector if your wiring is another configuration, not enough counterforce, put two of them in there.

QuoteDjDemonD
Please guys it may not be the (over)engineered solution you seek, but a keychain retractor is the answer. Very simple costs £2, works.

The way I use it is secured to the wiring loom, water cooling tubing, so it holds the effector up indirectly and keep my cable in a nice loop above the effector but you could attach it directly to the effector if your wiring is another configuration, not enough counterforce, put two of them in there.

Are these keychain retractors the little plastic ones with the nylon string used for ID badges, or are they the heavier and stronger ones that have a chain on them for holding a bunch of keys?

Had I heard about the keychain retractor before I started thinking about it I would certainly have used just that. In the end though I decided that I wanted a firm stowage for transport more than solving effector droop. The final part of the equation is to put a magnet between the hook and the trapeze to give it a bit more immunity against jolting - so far though a 4mm diameter magnet holds on to the hook like an angry chihuahua to a sock and stops it disconnecting for homing.

Mike.

p.s., I ordered a couple of the retractors anyway in case I find some downside in the piano wire idea.